A dry exhaust-gas treating apparatus for removing various harmful substances in an exhaust gas, such as SOx (sulfur oxide), NOx (nitrogen oxide), and so forth, by bringing the exhaust gas into contact with an adsorbent introduced into an adsorption tower has been known as an apparatus for treating the exhaust gas from a boiler, an incinerator, or a sintering furnace.
Examples of the adsorbent include a carbonaceous adsorbent, an alumina adsorbent, a silica adsorbent, and so forth. The carbonaceous adsorbent is excellent, because it can be treated at a relatively low temperature and remove various harmful substances at the same time. Examples of the carbonaceous adsorbent include activated carbon, activated coke, and so forth. Particularly, the adsorbent pelletized to a size of 0.5 cm to 4 cm is preferable. These adsorbents are well known.
In this apparatus, SOx in the exhaust gas is removed as sulfuric acid by adsorption to the adsorbent. Further, when ammonia is injected into the exhaust gas for pre-treatment, SOx is adsorbed as ammonium salts, and NOx is harmlessly reduced into nitrogen and water by catalysis of the adsorbent. The other harmful components are mainly adsorbed by the adsorbent and removed.
A large quantity of various substances such as sulfuric acid, ammonium salts, and so forth are attached to the adsorbent used for treating the exhaust gas in the adsorption tower, so that the adsorbent has low activity. For this reason, this adsorbent is transferred to a regeneration tower via a transfer passage such as a conveyor, heated and regenerated, and adsorbed substances are released from the adsorbent in the regeneration tower so as to restore the activity of the adsorbent to its original state.
The adsorbent whose activity is restored is transferred back to the adsorption tower via a transfer passage such as a conveyor. When the adsorbent is heated and regenerated, a gas (e.g. a carrier gas) for purging the substances released from the adsorbent may be used. For example, an inert gas such as nitrogen is used.
As a heating and regenerating method in the regeneration tower, a counterflow method of causing a desorbed gas, in which the adsorbed substances are released from the adsorbent, to flow in a direction opposite to a flow direction of the adsorbent that flows down in the regeneration tower standing in a tube shape is known. This counterflow method has an advantage in that initially released ammonia is barely present in the desorbed gas because the released ammonia is adsorbed to the adsorbent again (e.g. see Patent Documents 1 and 2).
As such, when the desorbed gas is sent to byproduct recovery equipment to produce a byproduct such as sulfuric acid or gypsum, it is possible to reduce a load of cleaning equipment, and thus this counterflow method is excellent. Here, the desorbed gas is adjusted so that its pressure is kept constant.
In the dry exhaust-gas treating apparatus disclosed in Patent Document 1, lock hoppers having excellent sealability are provided at both upper and lower ends of the regeneration tower. The lock hoppers regulate the flow of the adsorbent into and out of the regeneration tower, as well as the leakage of the desorbed gas from the regeneration tower and the introduction of oxygen into the regeneration tower.
Further, in the dry exhaust-gas treating apparatus disclosed in Patent Document 2, double rotary valves are disposed at both upper and lower ends of the regeneration tower. An inert gas is injected between the double rotary valves at each end of the regeneration tower. As in the case of Patent Document 1, the leakage of the desorbed gas from the regeneration tower and the introduction of oxygen into the regeneration tower are regulated by a sealing unit.    Patent Document 1: Japanese Patent Application Publication No. 2000-61253    Patent Document 2: Japanese Patent No. 3725013